Coronary computed tomography angiography (CCTA) using an intravenous contrast agent permits accurate noninvasive imaging of the anatomy of the coronary arteries.
CCTA can be used for the diagnosis of obstructive coronary artery disease in selected patients in whom image quality is presumed to be good.
CCTA is very sensitive in detecting obstructive coronary artery disease, and it is very suitable for excluding the disease.
In addition to stenosis, CCTA shows nonobstructive atherosclerosis not responsible for the patient's symptoms. Other examinations may be necessary to assess the significance of stenosis.
Appropriate patient selection is important to avoid unnecessary examinations.
Indications
CCTA is suitable for the exclusion of chronic obstructive coronary artery disease in selected symptomatic patients with low or increased pretest probability of the disease.
CCTA can be considered instead of exercise testing in symptomatic patients to exclude obstructive coronary artery disease despite an extremely low pretest probability.
CCTA can be considered as an alternative to catheter angiography to exclude coronary artery disease in selected patients before valvotomy or to investigate the cause of cardiac failure.
It is usually not recommended for detecting coronary artery stenosis in patients with previously diagnosed coronary artery disease or if good image quality is improbable because of irregular heartbeat or significant coronary calcification, for example.
CCTA is not recommended for systematic screening for coronary artery disease in asymptomatic patients.
Patient selection
The need for examinations to diagnose coronary artery disease should be considered based on clinical pretest probability.
The assessment of pretest probability in symptomatic people based on age, gender, number of risk factors and type of chest pain (see e.g. "Central illustration" in http://www.sciencedirect.com/science/article/pii/S0735109720373678) and local tools for assessing risk.
If obstructive coronary artery disease is suspected, diagnostic tests should be chosen based on assessment by a physician with expertise in the diagnosis and treatment of chronic coronary artery disease and on local protocols.
To obtain high quality images, the patient's heartbeat during imaging must be regular and calm. Therefore, CCTA is normally not recommended for patients with irregular heartbeat (frequent extrasystoles or atrial fibrillation) or rapid heartbeat that cannot be slowed down by medication. Significant overweight also affects the quality of imaging.
Significant calcification of coronary arteries complicates detecting stenosis on CCTA and may, in particular, lead to false positive findings. Therefore, CCTA is usually not recommended for patients with diagnosed coronary artery disease or generalized atherosclerotic disease. The probability of calcification of coronary arteries increases with age (66% of men and 47% of women over 65 have calcification in their coronary arteries), and in the elderly findings on CCTA are clinically less significant than in younger people.
Stenosis inside coronary stents is hard to detect on CCTA unless the stent diameter is large. Bypass grafts can be seen well on CCTA but it is difficult to assess any stenosis at graft seams or in recipient arteries that are often heavily calcified. Therefore, CCTA is usually not recommended for patients with a history of balloon angioplasty or bypass surgery.
In asymptomatic patients, CCTA will facilitate more accurate assessment of the risk of an arterial disease event compared to clinical assessment but treatment of risk factors based on imaging has not decreased the risk of such events compared to intervention based on clinical risk factors.
Scanning in practice
Coronary CT angiography is performed with a multislice computed tomography scanner with a minimum of 64 detector rows.
ECG-gating is used to do the scanning during the diastole phase of the cardiac cycle so as to avoid artefacts due to heart movements.
For this purpose, the heart rate during scanning must be < 65/min. Before scanning, the patient can be given a beta-blocker or other medication slowing down the heart rate, as necessary.
During scanning, the patient is asked to hold their breath for a few seconds.
To scan coronary arteries, an iodine-containing contrast medium is given as a rapid infusion into a peripheral vein.
Iodine allergy and renal failure must be considered, as well as an alternative diagnostic test for coronary artery disease, as necessary.
As CCTA exposes the patient to ionizing radiation, unnecessary examinations should be avoided and modern imaging technology with a reasonable 1-4 mSv radiation exposure should be used.
Interpretation of the scan requires expertise. Experience will reduce the number of unclear findings and particularly false positive findings.
The significance of findings
Coronary CT angiography is highly sensitive in detecting obstructive coronary artery disease (sensitivity and negative prognostic value > 95%), and it is very suitable for excluding the disease.
In addition to stenosis, CCTA shows nonobstructive coronary atherosclerosis not causing symptoms (Picture 1).
Assessment of the haemodynamic significance of stenosis may require additional examinations, either a non-invasive exercise test (exercise ECG Exercise Stress Test, myocardial perfusion test or exercise echocardiography) or invasive imaging applying a contrast medium and with the possibility for intracoronary manometry, as necessary.
Coronary CT findings may lead to unnecessary further investigations in patients with significant coronary calcification or poor image quality.
Abundant coronary atherosclerosis is a sign of a particularly high risk of arterial disease regardless of the level of stenosis, which should be considered when determining the aims for the treatment of risk factors (see Definition and Diagnosis of DyslipidaemiasTreatment of Dyslipidaemias).
In contrast with cholesterol-lowering medication, aspirin does not appear to improve the prognosis in patients diagnosed with coronary atherosclerosis but no obstructive coronary artery disease.
All patients diagnosed with obstructive coronary artery disease on CCTA should be prescribed medication improving the prognosis, as well as medication to alleviate the symptoms, as necessary Chronic Coronary Syndrome (Coronary Heart Disease).
Findings suggestive of a high risk of an arterial disease event include main stem stenosis, obstructive triple-vessel coronary artery disease and proximal left anterior descending coronary artery stenosis. High risk findings may indicate invasive contrast-enhanced imaging of the coronary arteries regardless of symptoms if revascularization (balloon angioplasty or bypass surgery) is considered to improve the prognosis.
Coronary calcification is a sign of atherosclerosis of the coronary arteries, which can be seen in CCTA also without contrast medium. Calcification of coronary arteries increases the pretest probability of obstructive coronary artery disease compared to clinical risk factors but imaging done without contrast agent cannot be used to diagnose or to exclude obstructive coronary artery disease.
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